The motivating force in Leonardo's life (1452-1519) was the study of nature, which he documented in thousands of pages of notebook entries. His explorations in a stunning range of fields--among them painting sculpture, botany, engineering, anatomy, geology, architecture, and music--made him the model of the "Renaissance man." One of the paradoxes of Leonardo's posthumous reputation as a painter is that there are remarkably few paintings definitely attributed to him, though one is among the most well known of all time. His passionate interest in nature is as evident in his few works as in his voluminous notebooks. The Mona Lisa, for example, takes a conventional portrait, which until that time had usually placed the sitter against a background of flat color, and gives the figure a mysterious mountain valley setting, not dissimilar to the landscape studies recorded in his journals. The landscape is barren, seemingly without evidence of human activity, until we notice a small bridge just over the right shoulder of the sitter. But a bridge to where? In this timeless, enigmatic landscape the extreme distance dissolves into the blue haze of accurately rendered atmospheric perspective.

This portrait is remarkable in a number of ways. The mysterious landscape in the background only reinforces the riddle of the sitter's smile, which has launched a thousand discussions. Breaking from previous portrait tradition, the sitter is shown in three-quarter profile, not from the side, and with both arms fully visible. She is both fully integrated into the landscape and set in front of it. The mist, typical of Leonardo, that seems to envelop the painting is called sfumato, or "smokiness." It melts form into form, softens the line, and adds volumetric nuances, a world away from the linear flatness of Botticelli. Enhancing the appeal of the portrait is the complex self-possession of the sitter, as she gazes out at the viewer in perfect serenity.